Since HK acquired Infinity a few years back they have used the line as a low to mid priced field for new technology. The drivers in the Primus series are mostly new designs and offer some interesting ideas. As an example, the efficiency of the speakers is generally higher than comparably sized pulp, poly or metal drivers while still achieving low frequency extension. Higher efficiency is always a good thing to have if you are not sacrificing the sound quality to get the numbers.
The only place I've had an opportunity to listen to the Primus was at Ultimate Electronics. Their listening rooms are set up much like every other chain store so the audition couldn't determine the speakers quality other than it had less "you expect me to pay money for that sound?" quality than many of the other brands lined up on the wall with the Infinity's.
Everyone listens for different qualities and every system and room present different challenges that will influence what speaker you prefer. The Infinity's would appear to be a good choice overall. They have what appears to be minimal interaction with the room so they should be very consistent from system to system.
I haven't gone back to check the measurements on the 150, but the 360 which was reviewed last month has a very benign impedance curve and phase angle. This should make it very amplifier friendly and well worth auditioning on your own amplifier. Too often when speakers (particularly budget speakers) are said to sound good, their electrical properties make them unuseable on low to mid priced equipment. This seems to be another mark in favor of the Infinity's.